Photocatalysts are utilized in recent years widely in various fields as they have deodorant, antiseptic, and antifouling functions. For example, when the ultraviolet light included in the sunbeam and others is irradiated on to the sheets containing photocatalyst particles, photo-redox reaction occurs so that the organic fouling or others attached on the surface of the sheet is decomposed. On the other hand, photocatalysts act not only on to fouling substances and others, but also decompose fibers and plastics themselves, so that it is considered to coat porous calcium phosphate which is inactive as a photocatalyst on the surface of titanium oxide as a photocatalyst. These were disclosed in Japanese Patent, JP 3275032 ([0006], [0009], reference 1), Japanese Patent Applications, JP 11-267519A ([0004], [0009], reference 2), JP 2000-1631A (Front page, reference 3) and JP 2000-119957A ([0009], reference 5) and PCT Application, WO01/017680 (Front page, reference 4).
FIG. 8 is a cross-sectional structural view of the conventional sheet containing photocatalysts. The conventional sheet 10 has a four layer structure as shown below. That is, the second layer 12 consisting of synthetic resins or rubbers is coated on the first layer 11 consisting of such fibers as synthetic fibers and inorganic fiber fabrics and others as a base. A middle layer 13 is coated on said second layer 12, and further a photocatalyst layer 14 having photocatalyst particles 15 such as titanium oxide or others on the middle layer 13 (for example, Japanese Patent Application, JP 10-237769 A ([0004], [0005], reference 6).
The middle layer 13 is located between the second layer 12 and the photocatalyst layer 14 so as not to deteriorate the resins and fibers composing the second layer 12 or the first layer 11 as the base, when the photocatalyst particles 15 contained in the photocatalyst layer 14 are photo-irradiated, and photo-redox reaction occurs. That is, the middle layer 13 functions as a sort of protective adhesive layer. Also, for fixing photocatalyst particles, such hardly decomposing materials as fluorocarbon resins and others are used.
FIG. 9 is a cross-sectional structural view of a sheet containing the photocatalysts different from those of FIG. 8. Although, in FIG. 8, a sheet 10 is coated in turn, on the surface of one side of the first layer 11, with the second layer 12, the middle layer 13, and the photocatalyst layer 14, there may also be a sheet 10a, as in FIG. 9, in which the second layer 12, the middle layer 13, and the photocatalyst layer 14 are coated symmetrically on both sides of the first layer 11.
As the method to weld the conventional sheets 10 and 10a, there may be method as shown below.
FIG. 10(a) is a cross-sectional view of the pre-step before welding the conventional sheet 10a, and (b) is a cross-sectional view of the welding step. In the pre-step shown in FIG. 10(a), a photocatalyst layer 14 and the middle layer 13 are removed by polishing or the like from all of the sheets 10a to be welded for the breadth d for mutually welding sheets 10a, thereby the adhesive resin layer as the second layer 12 is exposed on a surface on one side.
Next, at the welding step as shown in FIG. 10(b), the welding surfaces of breadth d are held together and thermally adhered. That is, the resins comprising the second layer 12 are molten and solidified together. As the methods of thermal adhesion, there may be hot blowing welding, hot plate welding, radio frequency welding, supersonic welding, and hot flatiron welding and others. Also, it may be possible to weld by using adhesives or double-stick tapes. Similarly for the sheet 10 the one side of which is coated with a photocatalyst layer 14, it is necessary for the photocatalyst layer 14 and the middle layer 13 of welding breadth d to be removed as the pre-step.
Thus, in case to weld sheets 10 and 10a for which photo-redox reaction by photocatalyst particles 15 has no bad influence on the second layer 12 and the first layer 11 due to the middle layer 13 located between the second layer 12 and the photocatalyst layer 14, it is necessary to remove the photocatalyst layer 14 and the middle layer 13 by welding breadth d (for example, Japanese Patent, JP 2889224 ([0007], reference 7)).
[Patent Reference 1] JP 3275032 ([0006], [0009]
[Patent Reference 2] JP 11-267519A ([0004], [0009]
[Patent Reference 3] JP 2000-1631A (Front page)
[Patent Reference 4] WO01/017680 (Front page)
[Patent Reference 5] JP 2000-119957A ([0009])
[Patent Reference 6] JP 10-237769 A ([0004], [0005])
[Patent Reference 7] JP 2889224 ([0007])
However, there may be such a problem that, if the middle layer 13 is located between the second layer 12 and the photocatalyst layer 14, process steps are increased for the manufacture of sheets 10 and 10a, thereby it causes low manufacturing efficiency and high cost.
There may also be a problem that, in case of mutually welding the conventional sheets 10 and 10a, a complicated process at the welding step is required in which the photocatalyst layer of welding breadth must be removed. There may also be a problem that, in case of fixing photocatalyst particles, such hardly decomposing materials as fluorocarbon and others are necessary to be used, thereby processing is difficult and cost is high.